PCAT Study Guide 2026

Bacteria are prokaryotic organisms, meaning they lack membrane-bound organelles, including mitochondria. Instead of mitochondria, bacteria perform cellular respiration using enzymes embedded in their cell membrane. Amoeba, fungi, and protozoans are all eukaryotic organisms and therefore possess mitochondria for energy production.

Hemoglobin has an affinity for carbon monoxide (CO) that is approximately 200-250 times greater than its affinity for oxygen. When CO is present, it preferentially binds to hemoglobin, forming carboxyhemoglobin and effectively preventing oxygen transport to tissues. This strong, stable binding is why carbon monoxide is highly toxic.

The plasma membrane is a selectively permeable phospholipid bilayer with embedded proteins that regulate what enters and exits the cell.

Logical structure with clear headings helps readers find information quickly and follow the progression of ideas effectively.

If the SA node stops operating, the heart will not instantly stop. Other parts of the cardiac conduction system, such as the AV node or Purkinje fibers, possess intrinsic automaticity and can take over as secondary pacemakers. While these secondary pacemakers generate impulses at a slower rate, they ensure that the heart continues to beat, preventing immediate cardiac arrest.

Lysosomes contain acid hydrolases that break down macromolecules and cellular debris in an acidic interior maintained by proton pumps.